[v10.0.x] Prometheus: Fix applying ad-hoc filters to the expression that has a template variable (#75300)

Prometheus: Fix applying ad-hoc filters to the expression that has a template variable (#75250)

* Interpolate first and then apply ad-hoc filters

* More tests

(cherry picked from commit d076f733e9)

Co-authored-by: ismail simsek <ismailsimsek09@gmail.com>

public/app/plugins/datasource/prometheus/datasource.test.ts

@@ -831,6 +831,55 @@ describe('PrometheusDatasource', () => {
       const result = ds.applyTemplateVariables(query, {});
       expect(result).toMatchObject({ expr: 'test{job="bar", k1="v1", k2!="v2"}' });
     });
+
+    it('should add ad-hoc filters only to expr', () => {
+      replaceMock.mockImplementation((a: string) => a?.replace('$A', '99') ?? a);
+      getAdhocFiltersMock.mockReturnValue([
+        {
+          key: 'k1',
+          operator: '=',
+          value: 'v1',
+        },
+        {
+          key: 'k2',
+          operator: '!=',
+          value: 'v2',
+        },
+      ]);
+
+      const query = {
+        expr: 'test{job="bar"} > $A',
+        refId: 'A',
+      };
+
+      const result = ds.applyTemplateVariables(query, {});
+      expect(result).toMatchObject({ expr: 'test{job="bar", k1="v1", k2!="v2"} > 99' });
+    });
+
+    it('should add ad-hoc filters only to expr and expression has template variable as label value??', () => {
+      const searchPattern = /\$A/g;
+      replaceMock.mockImplementation((a: string) => a?.replace(searchPattern, '99') ?? a);
+      getAdhocFiltersMock.mockReturnValue([
+        {
+          key: 'k1',
+          operator: '=',
+          value: 'v1',
+        },
+        {
+          key: 'k2',
+          operator: '!=',
+          value: 'v2',
+        },
+      ]);
+
+      const query = {
+        expr: 'test{job="$A"} > $A',
+        refId: 'A',
+      };
+
+      const result = ds.applyTemplateVariables(query, {});
+      expect(result).toMatchObject({ expr: 'test{job="99", k1="v1", k2!="v2"} > 99' });
+    });
   });
 
   describe('metricFindQuery', () => {

public/app/plugins/datasource/prometheus/datasource.tsx

@@ -1219,14 +1219,17 @@ export class PrometheusDatasource
     delete variables.__interval;
     delete variables.__interval_ms;
 
-    //Add ad hoc filters
-    const expr = this.enhanceExprWithAdHocFilters(target.expr);
+    // interpolate expression
+    const expr = this.templateSrv.replace(target.expr, variables, this.interpolateQueryExpr);
+
+    // Add ad hoc filters
+    const exprWithAdHocFilters = this.enhanceExprWithAdHocFilters(expr);
 
     return {
       ...target,
-      legendFormat: this.templateSrv.replace(target.legendFormat, variables),
-      expr: this.templateSrv.replace(expr, variables, this.interpolateQueryExpr),
+      expr: exprWithAdHocFilters,
       interval: this.templateSrv.replace(target.interval, variables),
+      legendFormat: this.templateSrv.replace(target.legendFormat, variables),
     };
   }